The United States is entitled to comment on Russian President Vladimir Putin's letter addressed to European leaders because it was openly published in Moscow, US State Department spokeswoman Jen Psaki said.

Psaki's words were her reaction to Putin's ironic remark a few hours ago that his letter had been meant for Russia's partners in Europe rather than Washington.

On Thursday, Putin sent a letter on the situation around Ukraine to the leaders of 18 European countries who buy Russian natural gas. In the letter, he explained in detail the current critical situation with Ukraine's debt for Russian gas supplies, which could affect gas transit to European consumers.

"It's no secret: helping the people of Ukraine: is a priority to the United States," Psaki told a daily press briefing on Friday. "I think commenting on a public letter is hardly an invasion of privacy."

Psaki seemed to have disregarded the ironic tone of Putin's statement. Speaking at a meeting of Russia's Security Council earlier Friday, the Russian president called Washington's reaction to his letter to European leaders "strange".

"It is strange because it is not nice to read letters addressed to other people," Putin said.

"The letter was not addressed to them but to European gas consumers. Everybody has got accustomed to the fact that our American friends tap conversations. But peeping and spying is not nice at all," Putin said jokingly, apparently hinting at recent high-profile spying scandals involving the US National Security Agency.

Putin again stated the essence of the problem, which consists in Ukraine's growing debt for Russian natural gas supplied to it, and the pre-default state of the country's economy.

Earlier, Psaki commented on Putin's letter and described Moscow's actions as an attempt to exert pressure on Kiev. "We condemn Russia's efforts to use energy as a tool of coercion against Ukraine," she said.

Ukraine is in political and economic turmoil following a coup that occurred in the country in February after months of anti-government protests triggered by Kiev's decision to suspend an association agreement with the European Union in November 2013 in favor of closer ties with Russia.

New people were brought to power in Kiev amid deadly riots that involved radicals after President Viktor Yanukovich had to leave Ukraine citing security concerns in February 2014. Russia does not recognize the new Ukrainian authorities.

Ukraine's crisis soured further when the Republic of Crimea, where most residents are Russians, refused to recognize the legitimacy of the new self-proclaimed Ukrainian authorities. Crimea held a referendum March 16 in which an overwhelming majority of Crimeans voted to secede from Ukraine and reunify with the Russian Federation. The accession deal with Moscow was signed two days later.

Moscow recently substantially raised the price for gas supplied to Ukraine from the figure of $268.5 per 1,000 cubic meters agreed last year when the association agreement with the EU was shelved in November 2013.

In the second quarter of 2014, the price for Russian gas for Ukraine was set at $385.5 per 1,000 cu m. Gazprom said earlier that the price rose from $268.5 due to the return to earlier contract agreements, as Ukraine failed to fulfill its commitments under an additional agreement concluded in December 2013, which obliged the country to pay for supplied volumes of Russian gas in time.

On April 2, Putin signed a law on denunciation of the Kharkov Accords with Ukraine, which were struck in 2010 and stipulated that Russia's lease of naval facilities in Crimea [then part of Ukraine] would be extended by 25 years beyond 2017 - until 2042.

The Kharkov deals envisioned a discount of $100 per 1,000 cu m on Russian gas for Kiev. Now that the accords have been denounced due to Crimea's accession to the Russian Federation, the discount will no longer be applied, raising the gas price by another $100 to $485.5 per 1,000 cu m.